The present invention relates to bearing cartridges, and in particular to bearing cartridges having a ferrofluid lubricant.
The use of ferrofluid bearings as an alternative to ball bearings is disclosed in U.S. Pat. No. 4,734,606 by the inventor of the present invention and incorporated herein by reference. Ferrofluid bearings have provided particular advantages over ball bearings when used in magnetic disk storage systems. More specifically, ferrofluid bearings tend to produce less audible noise than ball bearings. Furthermore, the use of ferrofluid bearings instead of ball bearings eliminates vibration produced by the inner ball bearing race, the outer ball bearing race and the ball bearings.
The use of a ferrofluid bearing in a disk spindle motor improves several performance factors of a magnetic disk storage device. Ferrofluid bearings tend to reduce or attenuate vibration originating in other parts of the disk storage device. In addition, ferrofluid bearings tend to have lower electrical resistance between the outer race and the inner race than ball bearings thereby providing a better discharge path to more rapidly dissipate any electrostatic charge that builds up on the disk surface. Furthermore, ferrofluid bearings tend to have a larger surface area between the bearing races over which to distribute shock loads, thereby withstanding mechanical shock better.
The ever increasing demands for greater memory capacity, lower production costs, faster memory access times, decreased size and weight of disk storage devices has placed increasing demands on the performance of the disk spindle motor. There is an increasing need for the bearing cartridges used in disk storage devices to provide improved performance factors such as reduced drag characteristics, improved ferrofluid containment and reduced manufacturing costs.